I do think that TACC should be free at the Model S/X price point, with the other Autopilot functionality a £2k upgrade, but I get that Tesla need the money so it's unlikely to happen.
With that said, their competition are catching up fast so I think they're going to have to respond soon or risk losing out.
Just take a look at the new Mercedes A class, it has TACC, lane keeping, auto-lane change (including checking it is safe to change) and a whole lot more, all as standard on the base model...